CVE-1999-1074

Step 1: Target Identification: The attacker identifies a Webmin instance running on a target system.

Step 2: Username Enumeration (Optional): The attacker may attempt to enumerate valid usernames, although this is not strictly necessary as the vulnerability allows brute-forcing any username.

Step 3: Password Guessing: The attacker uses a brute-force tool to repeatedly submit password guesses for a known or guessed username. Each attempt is sent to the Webmin login page.

Step 4: Authentication Bypass: Because there is no rate limiting, the attacker can submit an unlimited number of password attempts.

Step 5: Successful Login: Eventually, the attacker guesses the correct password, gaining access to the Webmin interface with the privileges of the compromised user.

The vulnerability lies in Webmin's authentication mechanism. Specifically, the software does not implement any rate limiting or account lockout policies after a certain number of failed login attempts. This allows attackers to repeatedly submit password guesses for valid usernames without any restrictions. The root cause is the absence of code that tracks failed login attempts and temporarily disables or restricts access for a user account after a threshold is reached. This oversight allows attackers to exploit the system's authentication process through a brute-force attack, making it susceptible to unauthorized access.